A method for preparing a particulate cathode material, and the material obtained by said method

Abstract

Disclosed are a method for preparing a complex oxide particle composition, the so-prepared particle composition and its use as electrode material. This composition comprises complex oxide particles having a non powdery conductive carbon deposit on at least part of their surface. Its method of preparation comprises nanogrinding complex oxide particles or particles of complex oxide precursors, wherein an organic carbon precursor is added to the oxide particles or oxide precursor particles before, during or after nanogrinding, and pyrolysing the mixture thus obtained; a stabilizing agent is optionally added to the oxide particles or oxide precursor particles before, during or after nanogrinding; and the nanogrinding step is performed in a bead mill on particles dispersed in a carrier solvent.

Description

FIELD OF THE INVENTION[0001]The invention relates generally to a method for preparing particle compositions, as well as the particles compositions obtained by said method, and uses thereof as electrode material.BACKGROUND OF THE INVENTION[0002]Lithium-ion batteries have known a phenomenal technical success and commercial growth since the initial work by Sony in the early 90's based on lithium insertion electrodes: essentially the high voltage cobalt oxide cathode invented by J. B. Goodenough and the carbon anode using coke or graphitized carbonaceous materials.[0003]Since then, lithium-ion batteries have progressively replaced existing Ni—Cd and Ni-MH batteries, because of their superior performances in most portable electronic applications. However, because of their cost and intrinsic instability under abusive conditions, especially in their fully charged state, only small cell size and format have been commercialized with success.[0004]In the mid 90's, Goodenough (See U.S. Pat. No...

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Problems solved by technology

However, because of their cost and intrinsic instability under abusive conditions, especially in their fully charged state, only small cell size and format have been commercialized with success.

As pointed out by Goodenough (U.S. Pat. No. 5,910,382 & U.S. Pat. No. 6,514,640), one drawback associated with the covalently bonded polyanions in LiFePO4 cathode materials is the low electronic conductivity and limited Li+ diffusivity in the material.

It is also known to improve conductivity of a phosphate powder when used as a cathode material, by intimately mixing conductive carbon black or graphite powder with the phosphate powder or the phosphate precursors before synthesis Such addition of carbon blakc or graphite powder involves usually relatively large quantities of C to achieve good connectivity and does not result in a good attachment of the C to the metal phosphate crystal structure, said attachment being a characteristic judged essential to maintain contact despite volume variations during long term cycling.

Problems remain however to optimize the processability, cost and performance especially when power, energy and cyclability are required simultaneously.

Manipulation and processing (coating and compacting) of elementary nanoparticles or their dispersion is more complex than manipulation and processing micron-size particles, given their large surfaces and low compaction.

However, sintering still occurs inside the large agglomerates and leads to limited power capability of an electrode made of said LiFePO4 / C.

Such dense and large particles made of agglomerates or aggregates lower the rate performance of the final products because of low Li+ diffusion and / or lack of conductive carbon inside the particles.

However, with time the nano particles tend to re-agglomerate due to strong van der Waals interaction or electrical double layer interaction.

In consequence, the particle size and particle morphology are complex to control.

Difficulties are often associated with the control of stoichiometry, crystallinity, phase purity and particle size.

In many of the processes reported so far, difficulties associated with the control of particle size, phase purity and carbon coating are the bottleneck to scale up the process.

It is difficult to achieve all optimized parameters in one single synthesis step.

During wet nanogrinding in isopropyl alcohol solvent, preliminary experiments on pure LiFePO4, obtained from a melt process, inventors were drawned to conclusion that such mechanical treatment present deleterious effects that affect the use of said pure LiFePO4 as a cathode material.

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